A friction mine hoist, which may be of the double or of the single conveyance type, may be characterized by a pulley with friction liners, or similar, grooved to the diameter of the head ropes. The conveyances (skip or cage) for a double friction hoist are carried by the head rope(s) with the head ropes laid over the pulley with a contact angle of about 180 degrees. The rope ends are secured to the conveyances. The friction between the head rope(s) and the friction liners allows for a certain difference in rope tension of the two sides of the pulley without the occurrence of rope slip. Balance/Tail rope(s) are attached under the conveyances to limit reduce the difference in rope tension between the two sides of the pulley. Traditionally the mass per meter of the balance ropes has been dimensioned to be equal or nearly equal to the mass per meter of the head ropes. Thereby the safety margin before rope slip occurs is independent or nearly independent of the position in the shaft of the two conveyances.
A single friction hoist is based on the same principle as a double friction hoist, but with the difference that one of the conveyances is replaced by a counterweight. The mass of the counterweight is normally selected to be equal to the conveyance mass plus 50% of the net load. Thereby the difference in rope tension between the two sides of the pulley at empty conveyance and at normal net load will be the same. Friction mine hoists can be ground mounted with head sheaves in the head frame or tower mounted with or without deflection sheaves.
The static load variations in the head ropes occur as a result of loading the conveyance at the lower stop level and then hoisting it to the unloading (dumping) level at the upper end of the shaft whereby the balance rope(s) add mass to the ascending conveyance side, so adding rope tension in the head rope(s). The load variations can either be expressed as differences in tension (MPa or psi) or as load variations in percent of the breaking load of the head rope(s).
The life of the head ropes of a mine hoist of the friction hoist type depends on several factors such as:                load distribution between the ropes in case of multi-rope arrangement        diameter ratio between the pulley and the ropes and between deflection sheaves or head sheaves and the ropes        the rope construction and wire tensile strength        the breaking strength of the rope        rope oscillations at loading and dumping (release) of the load        longitudinal and transverse rope oscillations        quasi stationary loads under acceleration and retardation        static load variations in particular near the rope ends (Static Load Range)        
Acceptable rope life is normally obtained for friction hoists in installations with hoisting distances up to 1400 to 1500 m by adopting applicable mine hoist regulations and good engineering practice.
At hoisting distances in excess of 1400 to 1500 m using friction hoists, the Static Load Range (SLR) increases to be the dominating factor determining the head rope life. Thereby, the SLR i.e. the maximum static load variation at the rope ends in percent of the rope breaking strength determines the limit for the practical/economical maximum hoisting distance for friction hoists. The SLR can be expressed by using the following equation:SLR (%)=(Nl+(z2*q2*H))*g*100/(z1*B) where
Nl=Net load (kg)
z2=the number of balance ropes
q2=the mass per meter of the balance ropes (kg/m)
H=the hoisting distance (m)
g=9.81 (m/s2)
z1=the number of head ropes
B=the breaking strength for the head ropes (N)